Semiconductor transistors, in particular field-effect controlled switching devices such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or an Insulated Gate Bipolar Transistor (IGBT), have been used for various applications including but not limited to use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Particularly with regard to power devices capable of switching large currents and/or operating at higher voltages, a low on-state resistance Ron and high breakdown voltages Ubd are often desired.
To achieve low on-state resistance Ron and high breakdown voltages Ubd, charge-compensation semiconductor devices were developed. The compensation principle is based on a mutual compensation of charges in n- and p-doped regions, which are often also referred to as n- and p-doped pillar regions, in the drift zone of a vertical MOSFET.
Typically, the charge-compensation structure formed by p-type and n-type regions is arranged below the actual MOSFET-structure, with its source, body regions and gate regions, and also below the associated MOS-channels that are arranged next to one another in the semiconductor volume of the semiconductor device or interleaved with one another in such a way that, in the off-state, their charges can be mutually depleted and that, in the activated state or on-state, there results an uninterrupted, low-impedance conduction path from a source electrode near the surface to a drain electrode arranged on the back side.
By virtue of the compensation of the p-type and n-type dopings, the doping of the current-carrying region can be significantly increased in the case of compensation components, which results in a significant reduction of the on-state resistance Ron despite the loss of a current-carrying area. The reduction of the on-state resistance Ron of such semiconductor power devices is associated with a reduction of the heat generated by the current in the on-state, so that such semiconductor power devices with charge-compensation structure remain “cool” compared with conventional semiconductor power devices.
Many power semiconductor devices including charge-compensation devices are usually designed as vertically conducting devices and have an active area (cell area) surrounded by a peripheral area. Accordingly, the electric current in the on state flows from the source on the front side to drain at the backside of the chip. The backside is often implemented as a “common-drain”, i.e. as an equipotential surface at drain potential.
However, there are applications which are better suited for common-source devices, i.e. to devices with one side implemented as an equipotential surface at source potential during device operation, or a combination of a common-source device with a common-drain device. Example refer to automotive applications and the integration of two semiconductor chips such as a power semiconductor field-effect transistor chip and a driver chip for the transistor chip or two power semiconductor field-effect transistor chips of a half-bridge or a synchronous rectifier circuitry into a common package.
Also due to similar voltage of gate and source structures during operation, these structures are often located in immediate “neighborhood” to each other and are processed from the same wafer side, namely the front side. However, if the wafer front side should represent a common source plane, the gate connection must be rewired to the wafer back side. Particularly in the case of high-voltage components (e.g. having a blocking voltage of at least one hundred volt), an edge-termination structure may than be required on the chip rear side (or in terms of production technology on the wafer back side). Unfortunately, the structuring and processing options are rather limited on the back of the wafer compared to the front side. Accordingly, it is often difficult to achieve sufficiently high blocking voltages for those devices, at least in a cost-efficient manner. Moreover, the rewiring of the gate connection through the bulk may also have an impact on the electric field distribution during device operation.
Accordingly, there is a need to improve field-effect semiconductor devices, in particular power field-effect semiconductor devices including charge-compensation field-effect semiconductor devices and manufacturing of those semiconductor devices.